In a linked meta-analysis, Stafford and colleagues (doi:10.1136/bmj.f185) provide evidence that cognitive behavioural therapy (CBT) may show some modest benefits in preventing transition to psychosis at 12 months’ follow-up in patients at high risk.1 In doing so, they summarise a huge amount of work on interventions to prevent psychosis. However, this approach assumes that a discrete state of high risk for psychosis exists, an assumption that has increasingly been challenged.

Traditionally, phenomena such as delusions and hallucinations (hereafter, psychosis) were thought to be diagnostic indicators of psychotic disorders such as schizophrenia. However, psychotic symptoms are more common than was previously realised. They are present—at various degrees of severity—in about 5% of the general population who are not seeking help; in about 25% of people with (non-psychotic) common mental disorders, such as anxiety and depression; and in around 80% of patients with psychotic disorders.2

Low grade psychotic phenomena in those not seeking help are associated with an increased relative risk—albeit low absolute risk—of later psychotic disorder, and, more surprisingly, also of non-psychotic mental disorder.3 Furthermore, low grade psychotic symptoms in people with common mental disorders predict a poorer prognosis, similar …

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